Water-swellable smectite clays have a great number of industrial uses that rely upon the ability of the clay to absorb many times its weight in water. Such water-swellable clays, such as sodium bentonite, however, lose much of their absorbency if the water absorbed is contaminated with water-soluble metal salts of alkali metals or alkaline earth metals, particularly the sulfate or halide salts, such as sodium chloride, magnesium chloride, calcium bromide, calcium chloride, potassium chloride, salt-containing body fluids and the like. Some bentonite clays, such as the blue bentonites disclosed in Clem U.S. Pat. No. 2,672,442, have required the uptake of calcium ions to provide acceptable water swellability and colloidal properties for industrial acceptance. The process of the present invention surprisingly provides bentonite clays, especially calcium bentonite and highly water-swellable sodium bentonite clays, with the sustained ability to absorb contaminated water and/or adsorb contaminants from the contaminated water.
The preferred smectite clays useful as starting materials in accordance with the present invention are non-blue sodium bentonites (green to greenish yellow to yellow to cream colored) that have industrially acceptable water swellability and colloidal properties and have a Fe.sup.+3 /Fe.sup.+2 ratio greater than 1, preferably at least 3, and most preferably in the range of about 5 to about 15. However, the process and product of the process of the present invention are useful to improve one or more characteristics, particularly contaminated water absorbency or adsorbency, of any smectite clay, particularly the highly water-swellable sodium bentonites for water absorbency, calcium bentonites for contaminant adsorbence, and blue bentonites, as will become more apparent from the data of the examples. Some of these industrial uses for the treated smectite clays of the present invention, where once dried clays, e.g., sodium bentonite, have their absorbency or contaminant adsorbency adversely affected upon contact with contaminated water, are described as follows.
Clem U.S. Pat. No. 4,021,402 discloses combining bentonite clay with a water-soluble polymer and a dispersing agent to enhance the absorption of salt-contaminated water. Alexander U.S. Pat. Nos. 4,613,542 and 4,624,982 disclose slurrying a water-swellable clay and a water-soluble anionic polymer in water to inhibit the swelling of the water-swellable clay for easier impregnation of a water-penetrable article with the clay slurry. Subsequent heating of the impregnated article breaks down the polymer to revert the clay to water-swellable. Slurrying of the clay in accordance with U.S. Pat. Nos. 4,613,542 and 4,624,982 completely hydrates the clay to a water content of at least 150%, based on the dry weight of the clay, and temporarily inhibits the water-swellability of the clay. This complete rewetting of the clay to such a high water content would not be useful in accordance with the present invention since the subsequent redrying step would be extremely costly and would impregnate the clay with a polymer solution that would be too dilute to achieve the advantages disclosed herein.
1. Drilling Muds
In drilling wells by rotary methods it is a common practice to circulate, continuously, a drilling mud or fluid into and out of a borehole during the drilling operation. The drilling mud is pumped into a drill pipe from a mud pit and the mud passes down to the bottom of the borehole. The drilling mud then flows upwardly through an annular space between the borehole wall and the drill pipe, and finally flows from the borehole through a mud ditch back to the mud pit, wherein the mud is mechanically or chemically treated before recirculation through the borehole.
The drilling mud serves several purposes that influence such factors as the drilling rate, cost, efficiency and safety of the operation. The drilling mud lubricates and cools the drill bit, acts as a vehicle to carry cuttings from the borehole, and provides sufficient equalizing hydrostatic pressure against the formation wall to prevent the borehole wall from cave-in during drilling. By using proper mud formulations, the borehole entry of gases and fluids encountered in the surrounding earthen formations pierced by the drill is inhibited and possible collapse or blowouts resulting from uncontrolled influxes of these formation fluids may be prevented. The drilling mud also exerts a "wall-building" effect whereby it often forms a thin filter cake on a borehole wall, thus sealing off the borehole and reducing water loss to the penetrated formations.
An acceptable mud must have body yet be free-flowing with relatively low viscosity in order to facilitate pumping. The mud must also have an acceptable gel strength in order to suspend solid material if circulation is interrupted and to prevent accumulation of solids at the drill bit to avoid mechanical jamming. Acceptable drilling muds may be either oil-based or water-based, and they are normally treated to provide the rheological properties that make them particularly desirable and useful for drilling wells. For example, drilling muds may be treated with barium sulfate (barite) or lead sulfide (galena) to increase their density.
The efficiency of the drilling process is related to the velocity of the mud flowing up the annular space between the borehole wall and drill pipe. This velocity is in turn related to the viscosity, density and flow properties of the mud. In addition, the drilling mud viscosity is known to depend upon the quality, concentration and state of dispersion of the colloidal solids of the mud. As the drilling operation proceeds, the rheological properties of the mud may be adversely affected by such factors as the nature of the drilled strata, loss or gain of water to the mud, chemically-active contaminants that may flocculate the mud, mud pH, and the increasing temperatures and pressures encountered at deeper drilling depths. In order to maintain workable viscosities, the muds must be formulated to respond to varying circumstances and conditions encountered during use. Since improvements in efficiency are realized as the viscosity and density of a mud are increased, it is desirable to optimize drilling mud formulations to possess the highest viscosity and density workably feasible for a given formation at a given depth.
Whenever possible, usually for reasons of economy, water-based drilling muds are used throughout the drilling operation. The suspending solids in water-based drilling muds are typically clays from the kaolinite, montmorillonite or ilite groups. These clays impart desirable thixotropic properties to the drilling mud and also coat the walls of the well with a relatively impermeable sheath, commonly called a "filter cake", that retards fluid loss from the well into the formations penetrated by the well. These properties of the suspended, water-swellable clays are substantially adversely affected by contact of the clay with salt-contaminated water resulting in less clay swelling and concomitant lower viscosity and more fluid loss.
An exemplary montmorillonite clay that can be used in a water-based drilling mud is a sodium bentonite. The bentonite is dispersed within the water-based liquid as colloidal particles and imparts various degrees of thixotropy to the drilling mud. Sodium bentonite, and other water-swellable bentonite clays, after processing by adding a water-soluble polymer to the clay and then rewetting the clay with water, and redrying, have excellent rheological properties for use in preparing aqueous drilling muds despite contact with contaminated water during the drilling process.
2. Lost Circulation Fluid
One difficultly often encountered in rotary drilling operations involves the loss of unacceptably large amounts of the drilling mud into a porous or cracked formation penetrated by the drill. The loss of drilling mud is termed "lost circulation", and the formation is termed a "lost circulation zone" or a "thief formation".
Lost circulation occurs when the well encounters a formation either having unusually high permeability or having naturally occurring fractures, fissures, porous sand formations, cracked or cavernous formations or other types of strata characterized by crevices, channels or similar types of openings conducive to drilling fluid loss. In addition, it is also possible for a formation to be fractured by the hydrostatic pressure of the drilling mud, particularly when a changeover is made to a relatively heavy mud in order to control high internal formation pressures.
When lost circulation occurs, the drilling mud pumped into the well through a drill string enters the cracks in a cracked formation or the interstices of a porous formation and escapes from the wellbore, therefore precluding return of the drilling mud to the surface. In the most severe situation, the lost circulation zone takes the drilling mud as fast as it is pumped into the wellbore, and, in the less severe situations, circulation of the drilling mud can be greatly reduced, and eventually result in a shutdown of drilling operations. Normally, the maximum amount of drilling mud loss that is tolerated before changing programs is approximately one barrel per hour. If a greater amount of drilling mud is lost, corrective measures are needed. Drilling generally is not resumed until the thief formation is closed off and circulation of the drilling mud reestablished.
The interruption of normal circulation prevents the removal, by entrainment, of cuttings and other materials from the borehole, leads to reduced hydrostatic pressure possibly followed by the influx into the wellbore of high pressure formation fluids, can result in the flooding of oil-producing zones with mud or the like, and may eventually cause the drill string to become stuck in the borehole. Even in situations where circulation is not completely lost and some drilling mud can return to the surface, the drilling mud flowing into the lost circulation zone must be replaced continuously. If the drilling mud loss is sufficiently high, the cost of continued drilling or well operation may become prohibitive. Therefore, the-lost circulation of drilling mud is a condition that must be prevented or be corrected as quickly as possible.
The best method of controlling lost circulation is to conduct a drilling program such that mud loss will not occur. However, situations exist wherein even correct drilling techniques cannot avoid lost circulation. Therefore, many methods have been used in attempts to plug the cracks or interstices of lost circulation zones to prevent the escape of drilling muds. As a result, a wide variety of materials have been pumped into the well with the drilling mud in an effort to bridge or fill the cracks or interstices of thief formations. It has been found that some materials are successful under certain drilling conditions, yet the same material is unsuccessful under other drilling conditions.
One common method is to increase the viscosity of the drilling mud or to increase the resistance of the drilling mud to flow into the formation. Another technique involves the addition of a bulk material, such as cottonseed hulls, cork, sawdust, perlite, ground walnut shells, hay, wood shavings, granular plastic, vermiculite, rock, mica flakes, leather strips, beans, peas, rice, sponges, feathers, manure, fish scales, corn cobs, glass fiber, asphalt, ground tires, burlap or other fabrics to the drilling mud. By adding these fibrous, flaky or granular solids to the drilling mud and pumping the resulting mixture into the borehole, a bridge or mat forms over the cracks or interstices responsible for drilling mud escape.
Although lost circulation zones frequently are plugged by such bulk materials, successful plugging of the thief formation is not assured. Even if large volumes of a solids-containing drilling mud are pumped into the borehole, a bridge or mat may never form over the cracks or interstices of the thief formation. Moreover, the introduction of large quantities of a drilling mud containing a relatively high percentage of bulky solids can produce pressure surges that cause further fracturing and therefore result in additional fissures for even greater drilling mud losses. Bulk materials also have proven unsuccessful in sealing off porous formations because they have a tendency to deteriorate under the high drilling pressures, and therefore decrease in volume and become slimy so as to "worm" into the formation openings without forming an effective seal.
Bentonite clay and a water-soluble polymer, mixed together, then rewetted with water in an amount sufficient to solubilize the polymer, thereby impregnating the rewetted clay with the polymer, followed by redrying the clay, as described in more detail hereinafter, gives the processed clay the ability to continue to increase the viscosity of aqueous liquids, with time, so that the clay will continue to swell upon entering the interstices of a thief formation for effective plugging despite contact with contaminated water during the drilling process.
3. Water Absorbency and Swellability
Water-swellable clays rewetted while the clay is in sufficient contact with a water-soluble polymer, so that the solubilized polymer impregnates the clay, and thereafter redrying the clay, in accordance with the principals of the present invention, provides the processed clay with new and unexpected water-absorbency and swellability when contacted with contaminated water, making the clays very useful for a number of industrial products and processes. The water-swellable clays rewetted to impregnate the clay with a water-soluble polymer, and redried in accordance with the principles of the present invention, provide unexpected water absorbency of contaminated water, and swellability upon contact with contaminated water making the clays very suitable for use in moisture impervious rigid and flexible water sealants or barriers, such as rigid or flexible panels, flexible water barriers formed by sandwiching the treated water-swellable clays of the present invention between two fabric layers, with or without needle-punching the fabric together, and the like; for preventing water contaminated with industrial waste, including metal salts, from seeping through soil containing one or more of the treated water-swellable clays; for waterproofing compositions in non-viscous sprayable forms, or paste or putty-like forms, capable of being applied by spray methods, caulking gun, or trowel; for use together with one or more elastomers and/or plasticizers for preventing the seepage of contaminated water through the compositions; together with other additives such as xanthan gum and/or other gums for maintaining stability in contaminated water; together with other components to manufacture a flexible grout composition for sealing drill holes contaminated with contaminated water; and for use as a water-swellable material in a layered water-sealing article of manufacture to prevent seepage of contaminated water therethrough.
4. Stabilization, Solidification and/or Thickening of Waste Sludges
Smectite clays, particularly smectite organoclays formed by reacting a smectite clay with a quaternary ammonium compound, are useful for physically trapping fluid wastes and spills, particularly organic wastes. For example, a smectite clay or an organophilic smectite clay can be mixed with aqueous or organic wastes for adsorption of the waste by the clay. ASTM Paint Filter Liquids Test #9095 tests the stabilized, thickened sludge to determine if any free liquid will fall through a supporting 60 mesh conical screen in 24 hours. Generally, about 5% to about 100% by weight smectite, based on the weight of the sludge, is mixed with the sludge for solidification. Usually an organophilic smectite clay is needed to sufficiently thicken a sludge containing organics to pass the Paint Filter Liquids Test #9095. Usually, about 10 to about 50 pounds of smectite clay is sufficient. The clays treated in accordance with the present invention can be used in lesser amounts than dry-mixed clay/polymer blends to pass ASTM Test #9095. The waste-containing clay then can be physically trapped in a solid matrix, e.g., by mixing the waste-containing clay with portland cement. Typical smectite clay-containing compositions for stabilization of waste sludges containing inorganic and organic waste materials are described in U.S. Pat. Nos. 4,650,590; and 4,149,968; hereby incorporated by reference.
The smectite clays treated in accordance with the present invention are useful in the absorption of water-dissolved contaminants and adsorption of organic wastes that are emulsified in water, for use in sludge solidification and sludge thickening.
5. Flocculation of Impurities From Waste Waters
Smectite clays, particularly sodium bentonite, have a long chain structure that provides sites, via the anionic clay charge, for adherence of inorganic contaminants, or for reaction to form an organoclay for adherence to multiple lipophilic sites, between smectite clay layers. By combining a cationic polymer, e.g., polyacrylamide, with the smectite or organophilic clay, anionic contaminants are attracted to the polymer, and the polymer is attracted to the clay platelets to flocculate the contaminants and clay together for easy removal of the floes. Examples of such separation of contaminants are found in U.S. Pat. No. 3,487,928; 2,367,384; and 4,517,094, hereby incorporated by reference.
The smectite clays treated in accordance with the present invention also are useful in the flocculation of contaminants and easier separation of the smectite flocs from the liquid.
6. Slurry Trenching
Smectite clays, such as highly water-swellable sodium bentonite clay, also are useful in slurry form (e.g., 1 part by weight clay for every 5 to 50 parts, usually 10 to 30 parts, water) to prevent the side walls of a trench from collapsing during excavation. The bentonite/water slurry is pumped into the trench during excavation and the clay from the slurry deposits on the excavated side walls and bottom wall or floor surfaces of the trench to hold the soil together at the excavated walls. The treated smectite clay of the present invention provides better results in slurry trenching to provide more structurally stable sidewalls when excavation uncovers contaminated water, and provides a surface clay cake on the excavated trench or on other dam walls to provide walls that are impermeable, or less permeable, to contaminated water.
Examples of these technologies and uses for the water-swellable clays rewetted, polymer-impregnated, and redried in accordance with the present invention are disclosed in the following U.S. Patents, all of which are hereby incorporated by reference: Clem U.S. Pat. Nos. 3,186,896; Clem 4,048,373; Clem 4,021,402; Clem 4,084,382; Clem 4,087,365; Clem 4,279,547; McGroarty 4,316,833; Piepho 4,332,693 and 4,462,470; Blais 4,344,722; Kingsbury 4,439,062; Harriett 4,534,925; Harriett 4,534,926; Alexander 4,634,538; Harriett 4,668,724; Harriett 4,696,698; Harriett 4,696,699; Alexander 4,886,550; Alexander 4,836,940; Harriett 4,733,989; Alexander 4,832,793; Harriett 4,810,573; Alexander 4,847,226; Colangelo 4,936,386 and 4,919,989; Alexander, et al. 4,919,818 and 4,944,634 and Alexander 5,112,665.
Excellent gel strength is achieved when water swellable bentonite, e.g., sodium bentonite, starting clays are processed in accordance with the present invention by combining the clay with a water-soluble polymer, rewetting the clay to solubilize the polymer and to impregnate the clay with the polymer, and then redrying the clay to a water content less than about 12% by weight. After processing by rewetting, polymer impregnating, and redrying, the clays are excellent suspending agents for use in the cosmetics and pharmaceutical industries in amounts well known in the art.